Mobile gateways in pool for session resilience

ABSTRACT

Embodiments of the invention include a method for providing UE session resilience performed in a first PDN-GW that is coupled to a second PDN-GW, which are both in a PDN-GW pool. The method provides UE session resilience by allowing the first PDN-GW to provide connectivity for UE sessions previously serviced by the second PDN-GW after the second PDN-GW becomes non-operational. The first PDN-GW recognizes that the second PDN-GW failed and then activates a plurality of standby UE sessions. Each standby UE session is a backup UE session corresponding to a previously active UE session serviced on the second PDN-GW. Each standby UE session is associated with a UE device and a network resource identifier of an APN slice. The first PDN-GW transmits a message to a SGW that is servicing the UE sessions that indicates that the SGW should direct traffic previously bound for the second PDN-GW to the first PDN-GW.

FIELD OF THE INVENTION

Embodiments of the invention relate generally to the field oftelecommunications; and more particularly, to mobile gateway pools.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) sets standards andtechnical specifications for a 3G mobile system referred to as Long TermEvolution (LTE). The LTE system includes an Evolved Packet System (EPS)with a main component called Evolved Packet Core (EPC). EPC comprisesthree main subcomponents: a Mobility Management Entity (MME), a servinggateway (SGW), and a packet data network gateway (PDN-GW). The 3GPPpublished “LTE; General Packet Radio Service (GPRS) enhancements forEvolved Universal Terrestrial Radio Access network (E-UTRAN) access,” TS23.401 Version 9.5.0 Release 9, defining the EPS service description.

In LTE, a user equipment (UE) device, such as a mobile phone,communicates with a SGW which in turn communicates with a PDN-GW. ThePDN-GW communicates further with an internet protocol (IP) service suchas an IP multimedia subsystem (IMS), voice over IP (VOIP), and mobilebroadband. The operator's IP services are provided over an IP-PDN thatis identified by a UE device with an access point name (APN). The seriesof communications between an APN and a UE device provide dataconnectivity to UE devices in the LTE mobile system and is referred toas a PDN connection. Thus, in each PDN connection, the PDN-GW couples anSGW with the APN and the SGW couples the UE device with the PDN-GW. Inthis scenario, each PDN connection (also referred to as a UE session)has corresponding PDN connection information (also referred to as UEsession information).

However, 3GPP's specification of LTE does not address some of themission critical aspects of EPC. For example, the specification does notaddress geographic redundancy, where one or more PDN-GWs or SGWs may belost. Nor does the specification address in-service maintenance, whereany PDN-GW or SGW must be brought out of service for maintenance.

Given that EPS targets full migration of voice services to IP-PDNs,operators are becoming more and more concerned with redundancyscenarios. 1+1 network level solutions exist, but such solutions areunnecessarily costly, since 50% of the available processing andforwarding capacity is used only for redundancy.

SUMMARY OF THE INVENTION

Embodiments of the invention include a method for providing userequipment (UE) session resilience performed in a first packet datanetwork gateway (PDN-GW) that is coupled to a second PDN-GW in a PDN-GWpool. The PDN-GW pool is to provide data connectivity between UE devicesand an external packet data network through an access point name. Themethod provides UE session resilience by allowing the first PDN-GW toprovide connectivity for one or more UE sessions previously serviced bythe second PDN-GW after the second PDN-GW becomes non-operational. Thefirst PDN-GW recognizes that the second PDN-GW is entering anon-operational state and activates a plurality of standby UE sessions.Each standby UE session is a synchronized UE session for which thesecond PDN-GW was the active PDN-GW. Further, each UE session isassociated with a UE device and a network resource identifier whichidentifies an APN slice that represents a subset of internet protocoladdresses in the external PDN. The first PDN-GW transmits a message to aSGW that is providing data connectivity between one or more of the UEdevices and the PDN-GW pool. The message indicates that the first PDN-GWhas activated standby UE sessions associated with one or more UE devicesserviced by the SGW. The first PDN-GW transmits the message with theintention that the SGW directs traffic previously bound for the secondPDN-GW to the first PDN-GW. In this way, UE session resilience isachieved in a PDN-GW pool by allowing the first PDN-GW to activate theplurality of standby UE sessions without notifying each UE deviceassociated with a standby UE session on the first PDN-GW.

Embodiments of the invention include a method performed in a servinggateway (SGW) for providing user equipment (UE) session resilience byallowing the SGW to reroute traffic between a packet data networkgateway (PDN-GW) pool from a first PDN-GW to a second PDN-GW. The SGW iscoupled to a first PDN-GW and a second PDN-GW, and the SGW is forproviding data connectivity between a UE device and the PDN-GW pool. ThePDN-GW pool provides data connectivity between the SGW and an externalPDN. The SGW creates a network resource identifier (NRI) map byinserting a plurality of NRI map entries in the NRI map. A first NRI mapentry associates a first NRI with the first PDN-GW as the active PDN-GWfor a first NRI. The first NRI is associated with a first slice of anaccess point name (APN) that represents a subset of internet protocoladdresses in the external PDN and the UE device is in communication withthe first slice of the APN. The SGW routes data traffic for UE sessionto the first PDN-GW, the UE session for traffic between the UE deviceand the first slice of the APN. The SGW receives a message indicatingthat the first PDN-GW entered a non-operation state. In response to themessage, the SGW updates the first NRI map entry to indicate anassociation between the first NRI and the second PDN-GW as the activePDN-GW for the first NRI. Further in response, the SGW routes datatraffic for the UE session to the second PDN-GW. In this way, UE sessionresilience is achieved by allowing the SGW to reroute data traffic fromthe UE device to an active PDN-GW without notifying the UE device of achange from the first PDN-GW to the second PDN-GW as the active PDN-GWfor that UE device's UE session.

Embodiments of the invention include a first packet data network gateway(PDN-GW) to be coupled to a second PDN-GW over a data tunnel in a PDN-GWpool. The PDN-GW pool is to provide data connectivity between anexternal PDN and a user equipment (UE) device. The first PDN-GW is toprovide UE session resilience by providing data connectivity for one ormore UE sessions previously serviced by the second PDN-GW after thesecond PDN-GE becomes non-operational. The first PDN-GW includes aprocessor and a set of one or more ports coupled to the processor and isfurther coupled to a serving gateway (SGW) pool and one or more accesspoint name (APN) slices, each APN slice representing a subset ofinternet protocol addresses in the external PDN. A memory is coupled tothe processor to store a plurality of active UE sessions and to store aplurality of standby UE sessions. Each active and standby UE session isto be associated with a UE device and a network resource identifier ofone of the one or more APN slices. The first PDN-GW further includes asession resilience module coupled to the memory to maintain theplurality of active UE sessions and standby UE sessions. The sessionresilience module is configured to recognize when the second PDN-GWenters a non-operational state. In response to recognizing when thesecond PDN-GW enters a non-operational state, the first PDN-GW is toactivate one or more of the plurality of standby UE sessions, eachactivated standby UE session to be associated with the second PDN-GW.The first PDN-GW is configured to further notify the SGW pool that thefirst PDN-GW has activated the one or more of the plurality of standbyUE sessions. In this way, UE session resilience is achieved by allowingthe first PDN-GW to activate a plurality of standby UE sessions withoutnotifying each UE device associated with a standby UE session on thefirst PDN-GW.

Embodiments of the invention include a serving gateway to be coupled toa user equipment (UE) device and a packet data network gateway (PDN-GW)pool comprised of a first PDN-GW and a second PDN-GW. The SGW is toprovide data connectivity between the UE device and the PDN-GW pool andprovide UE session resilience by allowing the SGW to reroute trafficbetween the PDN-GW pool and UE device from the first PDN-GW to thesecond PDN-GW. The SGW comprises a processor and a set of one or moreports coupled to the processor and to be coupled to one or more accesspoint name (APN) slices, each APN slice representing a subset ofinternet protocol addresses in the external PDN. The SGW furthercomprises a memory coupled to the process to store a network resourceidentifier (NRI) map configured to store NRI map entries that associatean NRI with an active PDN-GW, wherein each NRI identifies one or moreAPN slices. The SGW further comprises a session resilience modulecoupled to the memory. The session resilience module to maintain aplurality of UE session and maintain the NRI map. The session resiliencemodule configured to create a first NRI map entry to associate a firstNRI with the first PDN-GW as the active PDN-GW for the first NRI. Thesession resilience module further configured to route data trafficassociated with the first NRI to the first PDN-GW and configured toreceive notification that the first PDN-GW entered a non-operationalstate. The session resilience module further configured to update thefirst NRI map entry to associate the first NRI with the second PDN-GW asthe active PDN-GW for the first NRI and configured to route data trafficassociated with the first NRI to the second PDN-GW. In this way, UEsession resilience is achieved by allowing the SGW to reroute datatraffic from the UE device to an active PDN-GW without notifying the UEdevice of a change from the first PDN-GW to the second PDN-GW as theactive PDN-GW for that UE device's UE session.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereferences indicate similar elements.

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. In the drawings:

FIG. 1A is a block diagram illustrating a PDN-GW pool 102 implementingan N+M pooled resiliency scheme according to embodiments of theinvention.

FIG. 1B is a block diagram illustrating a SGW pool 103 implementing anN+M pooled resiliency scheme according to embodiments of the invention.

FIG. 2 is a flow chart illustrating a method for switching from a firstPDN-GW to a second PDN-GW as the active PDN-GW for an NRI according toembodiments of the invention.

FIG. 3 is a block diagram illustrating PDN-GW pool 102 responding to aPDN-GW failure according to embodiments of the invention.

FIG. 4 is a block diagram illustrating PDN-GW pool 102 responding to aPDN-GW going down for service according to embodiments of the invention.

FIG. 5 is a block diagram illustrating the resulting PDN-GW pool 102after the operations shown in FIG. 3 or 4 have been performed accordingto embodiments of the invention.

FIG. 6 is a block diagram illustrating PDN-GW pool 102 bringing up aninactive PDN-GW according to embodiments of the invention.

FIG. 7 is a block diagram illustrating a system including a PDN, a SGWpool, and a plurality of PDN-GWs (with one being shown in an explodedview) for providing N+M pooled session resilience according toembodiments of the invention.

FIG. 8 is a block diagram illustrating a system including a PDN-GW, a UEdevice, and a set of one or more SGWs (with one being shown in anexploded view) for providing N+M pooled session resilience according toembodiments of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details resourcepartitioning/sharing/duplication implementations, types andinterrelationships of system components, and integration choices are setforth in order to provide a more thorough understanding of the presentinvention. However, it is understood that embodiments of the inventionmay be practiced without these specific details. In other instances,well-known circuits, structures and techniques have not been shown indetail in order not to obscure the understanding of this description.Those of ordinary skill in the art, with the included descriptions, willbe able to implement appropriate functionality without undueexperimentation.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.“Coupled” is used to indicate that two or more elements, which may ormay not be in direct physical or electrical contact with each other,co-operate or interact with each other. “Connected” is used to indicatethe establishment of communication between two or more elements that arecoupled with each other.

Embodiments of the invention provide UE session resilience throughredundancy at the PDN-GW pools and the SGW pools. For each pool,embodiments of the invention provide geographic N+M redundancy and allowfor in-service maintenance of the PDN-GWs and the SGWs. N+M redundancywithin a pool allows up to M pool elements to be lost (with intermediatesession recovery using the methods described later) without impactingthe service for on-going UE sessions. As a PDN connection is created,each pool element stores UE session information corresponding that thatPDN connection. In one embodiment, the UE session information comprisesthe IP address assigned from the PDN to the UE device along withinformation identifying the PDN-GW and the SGW that is servicing the PDNconnection. Geographic N+M redundancy allows all PDN connections(connections between UE devices and DNs, also called UE sessions)serviced by a given pool element (PDN-GW or SGW) to have backup replicasof the corresponding UE session information evenly distributed over theremaining pool elements. In-service maintenance (including in-servicesoftware upgrades) occurs by bringing a pool element in or out ofservice without impacting ongoing UE sessions. While geographicredundancy can be used for this purpose, the implied failover to abackup node generally causes unnecessary disturbances; hence the need touse a smoother mechanism for maintenance.

The general strategy may be further understood through the embodimentshown in FIG. 1A. FIG. 1A is a block diagram illustrating a PDN-GW pool102 implementing an N+M pooled resiliency scheme according toembodiments of the invention.

At the top of the Figure, a plurality of PDNs 190 are illustrated asthree clouds. The PDNs are coupled to PDN-GWs, and in FIG. 1A, the firstPDN, which is assigned as APN 101, is coupled to a PDN-GW pool 102. APNstypically consist of two parts: a network identifier and an optionaloperator identifier. The network identifier of an APN identifies the PDNthe UE device 106 is coupling to through a PDN connection; typical APNnetwork identifiers correspond with the IP services desired by the UEdevice 106 such as General Packet Radio Services, Internet, andMultimedia Messaging Service. In the example of FIG. 1A, APN 101 isassigned to a PDN that contains a plurality of IP addresses,10.0.0.1-10.0.0.144, and APN 101 is sliced into 16 APN slices 101 a-101p. Each APN slice 101 a-101 p is assigned to a network resourceidentifier (NRI) and encompasses a subset of the plurality of IPaddresses within the PDN. The multiple APN slices may be assigned to thesame NRI and this is fully configurable. In FIG. 1A, the exemplary APNslice assignments are:

1. APNs 101 a and 101 b assigned to NRI 1;

2. APN 101 c assigned to NRI 2;

3. APN 101 d assigned to NRI 3;

4. APN 101 e assigned to NRI 4;

5. APN 101 f assigned to NRI 5;

6. APNs 101 g-101 i assigned to NRI 6;

7. APN 101 j assigned to NRI 7;

8. APN 101 k assigned to NRI 8;

9. APNs 101 l-101 m assigned to NRI 9;

10. APN 101 n assigned to NRI 10;

11. APN 101 o assigned to NRI 11; and

12. APN 101 p assigned to NRI 12.

As described above, APN 101 is coupled to PDN-GW pool 102 through dataconnection 110. The exemplary PDN-GW pool 102 comprises 4 PDN-GWs102A-102D, although other embodiments may utilize fewer or more PDN-GWs.Each PDN-GW 102A-102D is assigned an IP address 10.0.1.10, 10.0.1.20,10.0.1.30, and 10.0.1.40 respectively. In one embodiment, each PDN-GW102A-102D is optionally coupled to each of the other PDN-GWs 102A-102Dthrough data connections 120A-120F.

In FIG. 1A, each PDN-GW is servicing a plurality of active UE sessions.For example, when a UE device 106 forms a PDN connection with the PDNidentified as APN 101 that UE device will be coupled to an IP address inone of the NRIs. If, for example, the UE device is coupled with an IPaddress in NRI 1 then the UE device will have an active UE session onPDN-GW 102A which is servicing active sessions for NRI 1. The UEsessions are not shown in FIG. 1A as many sessions, both active andstandby, may exist for each NRI on the PDN-GWs, active and standby, thatare servicing that NRI.

Each PDN-GW 102A-102D has is servicing active UE sessions for three NRIswithin APN 101. PDN-GW 102A is servicing active UE sessions coupled toNRI 1, NRI 2, and NRI 8. PDN-GW 102B is servicing UE sessions coupled toNRI 3, NRI 4, and NRI 10. PDN-GW 102 c is servicing UE sessions coupledto NRI 5, NRI 6, and NRI 11. PDN-GW 102D is servicing UE sessionscoupled to NRI 7, NRI 9, and NRI 12. It should be understood, that eachPDN-GW could service more or less APN slices assigned to the NRIs.Furthermore, each PDN-GW could service multiple UE sessions, eachcorresponding to a different UE device, assigned to the same NRI.

Each PDN-GE 102A-102D is also servicing a plurality of standby UEsessions that each correspond to an active UE session serviced by one ofthe other PDN-GWs 102A-102D. PDN-GW 102A is servicing standby UEsessions coupled to NRI 4, NRI 5, and NRI 7. PDN-GW 102B is servicingstandby UE sessions coupled to NRI 1, NRI 11, and NRI 12. PDN-GW 102 cis servicing standby UE sessions coupled to NRI 2, NRI 3, and NRI 9.PDN-GW 102D is servicing standby UE sessions coupled to NRI 6, NRI 8,and NRI 10. Thus, in the embodiment of FIG. 1A, each PDN-GW 102A-102D isservicing standby UE sessions coupled to three different NRIs. Each ofthese standby UE sessions correspond to active UE sessions which arebeing serviced by one of the other PDN-GWs.

As time goes by, each PDN-GW 102A-102D receives session informationcorresponding with the standby UE sessions that PDN-GW is servicing. Asthe standby UE sessions are created, these sessions are maintained insynchronization with the corresponding active UE sessions such that thePDN-GW pool 102 is prepared to handle the failure of a PDN-GW. In oneembodiment, this information is communicated between PDN-GWs 102A-102Dacross data connections 120A-120D. These data connections 120A-120D maybe dedicated links between two PDN-GWs 102A-102D or may be a secondarynetwork topology coupling the PDN-GWs 102A-102D so that communication ofUE session information does not hamper the existing communicationchannels. Data connections 120A-120D are shown in dashed lines toindicate the links can be dedicated to synching session information ormay be general purpose data connections that also carry the sessioninformation.

The PDN-GW pool 102 is further coupled to an SGW pool 103 through dataconnection 111. The exemplary SGW pool 103 is comprised of three SGWs103A-103C, although other embodiments may utilize less or more SGWs.Each SGW 103A-103C couples one or more of the UE devices 106 with thePDN-GW pool 102, thus each SGW 103A-103C services a plurality of UEsessions. SGW 103A has UE sessions for UE devices coupled with NRI 1,NRI 2, NRI 4, and NRI 11. SGW 103B has UE sessions for UE devicescoupled with NRI 3, NRI 5, NRI 6, NRI 7, and NRI 12. SGW 103C has UEsessions for UE devices coupled with NRI 5, NRI 8, NRI 9, NRI 10, andNRI 12. Each SGW 103A-103C has an NRI map with NRI map entriesindicating, at least, the active PDN-GW for each NRI. In anotherembodiment, the NRI map entries further identify a standby PDN-GW foreach NRI as shown in the dashed ovals in the SGWs 103A-103C of FIG. 1A.In one embodiment, each SGW 103A-103C is coupled with each of the otherSGWs 103A-103C across data connections 124A-124C. The SGWs 103A-103C arecoupled, through data connections 125A-125C, to one or more basestations 105 further coupling the SGWs 103A-103C with the UE devices106. Each of the UE devices 106 is associated with an IP address thatresides in one of the slices of APN 101.

In one embodiment, FIG. 1A further includes an MME 115 coupled to thePDN-GW pool 102 through data connection 122 and coupled to the SGW pool103 through data connection 123. The MME is responsible for trackingidle UE devices and performing UE device reachability procedures.According to 3GPP TS 23.401, the MME assigns one of the SGWs 103A-103Cand one of the PDN-GWs 102A-102D for each PDN connection. In embodimentsof the invention, the PDN-GWs 102A-102D correspond to NRIs and thus theMME assigns an NRI for a PDN connection which dictates the responsiblePDN-GW. Optionally, the MME includes a session resilience module 116that assigns PDN-GWs 102A-102D as active or standby PDN-GWs for the NRIs1-12. The session resilience module 116 further transmits NRI map entryinformation to the SGWs 103A-103C to inform each SGW which PDN-GW isserving as active PDN-GW and which PDN-GW is serving as standby PDN-GWfor a given NRI. Furthermore, the session resilience module 116transmits indications to the SGWs 103A-103C to switch from an activePDN-GW to a standby PDN-GW for a given NRI in response to a PDN-GWentering a non-operational state. In a further embodiment, sessionresilience module 116 is responsible for transmitting updated UE sessioninformation from one of the PDN-GWs 102A-102D to the standby PDN-GW forthat UE session. Optionally, the MME 115 also includes a heartbeatmodule 117 that transmits status inquiry messages to the PDN-GWs102A-102D and notifies the session resilience module 116 in the eventthat a PDN-GW fails to respond to the status inquiry message. While someembodiments includes the MME 115, in alternative embodiments of theinvention the MME operations are performed by another entity (e.g., inone of the PDN-GWs, one of the SGW, distributed between one PDN-GW andone SGW, distributed over multiple of the PDN-GWs, distributed overmultiple of the SGWs, distributed over multiple of the SGWs).

In FIG. 1A, each PDN-GW and each SGW is associated with an IP addressthat is indicated above the corresponding element in brackets. Forexample, PDN-GW 102A is associated with 10.0.1.10 as its IP address.However in another embodiment of the invention, each NRI has an IPaddress in the PDN-GW pool. In this embodiment, the PDN-GW servicing UEsessions for each NRI receives data traffic designated for that NRIs IPaddress. In either case, the PDN-GW pool exports routing informationprotocol (RIP) information indicating the active PDN-GW IP address asthe next hop for IP addresses in each corresponding NRI. In oneembodiment utilizing a single IP address for each PDN-GW, the RIPinformation further indicates the standby PDN-GW IP address as the nexthop for IP address in each corresponding NRI. In the embodimentincluding both an active and standby PDN-GW, the metric (or statisticsassociated with the metric such as communication cost, hop count,network delay, path cost) associated with the active PDN-GW isconsiderably less than the metric associated with the standby PDN-GW toensure that traffic is routed to the active PDN-GW.

In FIG. 1A, the NRI maps in the SGWs 103A-103D identify each PDN-GW102A-102D by the corresponding letter A-D. In one embodiment, the NRImaps identify each PDN-GW 102A-102D by that PDN-GW's IP address, e.g.10.0.1.20 for PDN-GW 102B. In embodiments for which each NRI has an IPaddress in the PDN-GW pool, the NRI IP address is used in the NRI map toindicate which IP address traffic is directed for a given NRI.Furthermore, although the figures show each PDN-GW and SGW as identifiedby a letter, other embodiments can use any number of differentidentifier types (e.g., assign a non-negative pool element identifier toeach pool element for identification purposes). In embodiments utilizinga plurality of IP address for each pool element, the PDN-GW pool and theSGW pool maintains a pool element identifier map indicating which IPaddresses correspond to each pool element and NRI.

When a PDN connection between a PDN and a UE device is first created, anumber of selections must be performed. The MME initially selects an SGWto service the PDN connection and transmits a GTP-C Create SessionRequest to the SGW. If one of the SGW already serves one or more PDNconnections for the same UE device then the same SGW as for those PDNconnections is used. Otherwise, any SGW may be used with a preferencetoward balancing all PDN connections across the available SGWs.

Further, when a PDN-GW receives a PDN connection request (also called aGTP-C Create Session Request) if the PDN-GW is servicing one or moreNRIs associated with an APN slice of the selected APN then the PDN-GWselects one of the associated NRIs and allocates an IP address in thatNRI for the PDN connection. If the PDN-GW is not servicing an NRIassociated with a slice of the selected APN then the PDN-GW has twooptions. One, the PDN-GW can use a preconfigured APN slice map todetermine an NRI to use and allocate an associated IP address for thePDN connection. Two, the PDN-GW can determine if another one of thePDN-GWs is servicing an NRI in the APN and forward the PDN connectionrequest to the other PDN-GW.

In one embodiment, a typical PDN connection follows the following stepsonce the SGW selection and PDN-GW selection occurs. First, a GTP-CCreate Session Request is sent from the MME to the selected SGW. A GTP-CCreate Session Request is sent from the selected SGW to the selectedPDN-GW. The PDN-GW becomes the active PDN-GW for that UE session andresponds to the selected SGW with a GTP-C Create Session Responseindicating that it will act as the active PDN-GW and includes thatPDN-GW's IP address. The selected PDN-GW also forwards the GTP-C CreatesSession Request to the standby PDN-GW for the corresponding NRI and thestandby PDN-GW forwards a GTP Session Response to the selected SGW thatindicates it will act as the standby PDN-GW and that includes thatPDN-GW's IP address. The selected SGW records the active PDN-GW's IPaddress and the standby PDN-GW's IP address in an NRI map entry. Theselected SGW then sends a GTP-C Create Session Response to the MME.

The methods and embodiments are described with reference to maintainingactive and standby UE sessions on the PDN-GW and maintaining associatedNRI maps on the SGWs. However, one skilled in the art would recognizethat alternative embodiments allow for the active and standby UEsessions on the SGW and maintenance of associated NRI maps on thePDN-GWs. In such a case, the same session resilience achieved at thePDN-GW pool 102 would be achieved at the SGW pool 103 with similarmethods and embodiments. For example, FIG. 1B is a block diagramillustrating a SGW pool 103 implementing an N+M pooled resiliency schemeaccording to embodiments of the invention. This figure is essentiallyidentical to FIG. 1A except that each SGW, rather than the PDN-GW, isservicing a plurality of active UE sessions and a plurality of standbyUE sessions. As similar to FIG. 1A, each NRI is serviced by two SGWs.One SGW acts as an active SGW for an NRI and another SGW acts as astandby SGW for that NRI. Further, as similarly described with referenceto the SGWs 103A-103C in FIG. 1A, each PDN-GW 102A-102D has an NRI mapwith NRI map entries indicating, at least, the active SGW for each NRI.In another embodiment, the NRI map entries further identify a standbySGW for each NRI as shown in the dashed ovals in the PDN-GWs 102A-103Dof FIG. 1B. Thus, session resilience may be provided at the SGW pool 103in a similar manner as the PDN-GW pool 102.

FIG. 2 is a flow chart illustrating a method for switching from a firstPDN-GW to a second PDN-GW as the active PDN-GW for an NRI according toembodiments of the invention. This figure includes steps that areoptional depending on the specific implementation and such steps areshown with dashed boxes. A first PDN-GW, such as PDN-GW 102A, recognizesthat a second PDN-GW, such as PDN-GW 102C, is entering a non-operationstate (Block 200). In this case, the second PDN-GW 102C is servicing oneor more active UE sessions and the first PDN-GW 102A is acting as astandby PDN-GW for at least one of the active UE sessions. The firstPDN-GW 102A may recognize the entry into the non-operational state in anumber of ways. In one embodiment, the first PDN-GW 102A receives amessage that notifies it that the second PDN-GW 102C is entering anon-operational state. In another embodiment, the first PDN-GW 102Aincludes a heartbeat mechanism or other such mechanism that periodicallyverifies that the second PDN-GW 102C is still active and is thus able torecognize when the second PDN-GW 102C enters a non-operational state. Anon-operational state may arise because a PDN-GW has experienced somesort of failure or may arise because a PDN-GW is being intentionallytaken down for maintenance.

In the case where a PDN-GW is being intentionally taken down formaintenance, it is desirable to controllably initiate the handoff of UEsessions from the active PDN-GW to the standby PDN-GW through a gracefulswitchover. In this scenario, a temporary data tunnel may be establishedfrom the first PDN-GW 102A and the second PDN-GW 102C (Block 210). Insuch a scenario, the second PDN-GW 102C (the PDN-GW going from theactive state to a non-operational state) may forward all trafficassociated with the active UE sessions moving to the first PDN-GW 102Ato the first PDN-GW 102A over the temporary data tunnel. In this way,the UE device(s) will not experience a service interruption while thePDN-GW and SGW switch from second PDN-GW 102C to the first PDN-GW 102A.Furthermore, the first PDN-GW 102A will receive UE session informationfrom the second PDN-GW 102C for all UE sessions being moved from thesecond PDN-GW 102C to the first PDN-GW 102A to ensure that the firstPDN-GW 102A has the most recent session information (Block 220). Thisinformation will be used to update the session information for thecorresponding standby UE sessions.

In the case of a failure or intentional take down of a PDN-GW, themethod continues with the first PDN-GW 102A activating a plurality ofstandby UE sessions. Each of the activated standby UE sessionscorresponds with a previously active UE session that was serviced by thesecond PDN-GW 102C (Block 230). A message is transmitted to a SGWindicating that the first PDN-GW 102A has activated the plurality ofstandby UE sessions (Block 240). In one embodiment, the SGW receives amessage indicating a new NRI map and, thus, determines which UE sessionsshould be redirected from the second PDN-GW 102C to the first PDN-GW102A. In another embodiment, the SGW receives a message indicating thatsecond PDN-GW 102C has entered the non-operational state and the SGW isexpected to react by switching to the standby PDN-GW(s) for all UEsessions previously serviced by the second PDN-GW 102C. In anotherembodiment, the SGW receives a message indicating a plurality of NRIsthat must switch from the active PDN-GW 102C to the standby PDN-GW(s)(e.g., 102A) and the SGW is expected to switch the UE sessionscorresponding to those NRIs from the previously active PDN-GW 102C tothe newly active PDN-GW(s) (e.g., 102A) for those UE sessions. In yetanother embodiment, the SGW receives a message from the PDN-GWs thathave activated standby UE sessions indicating that the SGW shouldwithdraw the GTP-Path to the failed PDN-GW. In the scenario of agraceful switchover, the second PDN-GW 102C will either expect the SGWsto switch over after a given period of time or receive some indicationthat SGWs have completed the switch over and, in response to the timeperiod or indication, the temporary data tunnel will be closed (Block250).

This method is particularly advantageous because of how well it scalesregardless of the number of UE devices in the system. Upon the secondPDN-GW entering a non-operational state, there is no need to send aseparate message for each UE device to each SGW to notify the SGW of theswitch to the standby PDN-GW(s). Rather, each affected SGW in the SGWpool will handle the switch to the standby PDN-GW(s) seamlessly withouteach UE device experiencing a change regarding the PDN connection. Thus,embodiments of the invention address mission critical aspects of the EPCby providing session resiliency and geographic redundancy, where one ormore PDN-GWs or SGWs may be lost without affecting existing UE sessions.Further, because embodiments of the invention allow for N+M redundancy,there is less wasted available processing and forwarding capacity asredundancy is spread across the PDN-GW pool 102 and SGW pool 103depending upon the implementation.

FIG. 3 is a block diagram illustrating PDN-GW pool 102 responding to aPDN-GW failure according to embodiments of the invention. This figure isidentical to FIG. 1A except that it includes a plurality ofpoints/operations and change indications that occur in response toPDN-GW 102C failing (indicated in the figure with a bold X throughPDN-GW 102C). Point 1 indicates that PDN-GW 102C has entered into anon-operational state. The example given in the figure is a hardwarecrash, though any unexpected failure may cause PDN-GW 102C to enter afailure mode. In this embodiment, PDN-GW 102C is servicing UE sessionscoupled to NRIs 5, 6, and 11. At point 2 a and 2 b, the PDN-GW 102C'sfailure is detected either by the heartbeat module 117 in the MME 15 (asindicated by 2 a) or is detected in the PDN-GW pool (as indicated by 2b). Point 3 shows that each PDN-GW 102A, 102B, and 102D movescorresponding UE sessions from standby to active status; this is shownwith a box around the NRI with an arrow showing the NRI was moved fromstandby to active and an X through the NRI in the standby section of thePDN-GW. In the illustrated example, PDN-GW 102A was servicing standby UEsession(s) for NRI 5 for PDN-GW 102C and moves those sessions intoactive status; PDN-GW 102B was servicing standby UE session(s) for NRI11 for PDN-GW 102C and moves those sessions into active status; andPDN-GW 102D was servicing standby UE session(s) for NRI 6 for PDN-GW102C and moves those sessions into active status. In point 4, theremaining PDN-GWs 102A, 102B, and 102D take over responsibility forPDN-GW 102C's standby UE session(s) by creating new standby UEsession(s) (indicated in the figure with underlining) for the NRIs thatPDN-GW 102C previously serviced standby UE sessions. In the illustratedexample, PDN-GW 102A creates new standby UE sessions for NRIs 3 and 11;PDN-GW 102B creates new standby UE sessions for NRIs 6 and 9; and PDN-GW102B creates new standby UE sessions for NRIs 2 and 5. Point 5 indicatesthat the SGW pool 103 receives either new NRI maps or indications as tothe changes required to the NRI maps because of PDN-GW 102C's failure.All NRI map entries previously indicating PDN-GW 102C as the activePDN-GW must be updated to indicate the PDN-GW servicing the newlyactivated UE sessions for the corresponding NRI. In the illustratedexample, the active PDN-GW must be updated for all entries correspondingwith NRIs 5, 6, and 11. In one embodiment, the NRI map also includesstandby PDN-GWs in the NRI map entries and those entries indicatingPDN-GW 102C as the standby PDN-GW must be updated to indicate the PDN-GWthat took over responsibility for those standby UE sessions (i.e., thosePDN-GWs that created new standby UE sessions for the correspondingNRIs). In FIG. 3, the updated NRI map entries are bolded and underlinedto indicate that a new PDN-GW is indicated by the NRI map.

In embodiments for which each NRI has an IP address in the PDN-GW pool,point 5 behaves in a different fashion. Specifically, it is notnecessary for the NRI map entries to be updated since the IP addressassociated with an NRI will not change. Rather, as each PDN-GW activatesstandby UE sessions corresponding with an NRI, that PDN-GW also beginsreceiving traffic from the SGWs and the PDN destined for that NRI's IPaddress. In these embodiments, it is not required for the SGW tomaintain an active/standby NRI map as all that is required is that theSGW maintain an association with an NRI and that NRI's IP address. Inone embodiment, each UE session includes the IP address of the PDN-GWservicing that UE session. In this embodiment, the IP address in the UEsession is the NRI's IP address and no NRI map is required as the IPaddress will be serviced by another PDN-GW upon the failure of thePDN-GW servicing the NRI. In this embodiment, PDN connections areassociated with the NRI's IP address rather than the PDN-GW's specificIP address.

In embodiments utilizing a single IP address per PDN-GW rather than anIP address per NRI, the method continues by updating the routes to eachAPN slice. At point 6, new APN slice routes (e.g., RIP information) isexported from the PDN-GW pool to the applicable PDN indicating thePDN-GW IP address as the next hop for each of NRIs previously servicedby the failed PDN-GW. In embodiments with standby PDN-GWs, the RIPinformation for the standby PDN-GW was previously exported and all thatis required is for the metric of the standby PDN-GW route be lowered andthe metric of the previously active PDN-GW be raised such that the routeto the newly active PDN-GW is preferred according to routing algorithms.Upon creating new standby UE sessions, new RIP information is generatedfor each NRI and the PDN-GW that is taking over as the standby PDN-GWfor that NRI. This RIP information is exported with a higher metric thannewly active RIP information and with a lower metric than the previouslyactive RIP information.

FIG. 4 is a block diagram illustrating PDN-GW pool 102 responding to aPDN-GW going down for service according to embodiments of the invention.This figure is identical to FIG. 1A except that it includes a pluralityof points/operations and change indications that occur in response toPDN-GW 102C going down for service (indicated in the figure with adashed X through PDN-GW 102C). In this figure, PDN-GW 102C is going down(e.g. for service updates) at point 1. Point 2 shows that temporary datatunnels are established between PDN-GW 102C and each of the otherPDN-GWs 102A, 102B, and 102D as each is servicing standby UE sessionscorresponding to PDN-GW 102C. The temporary data tunnels are shownacross data connections 120D (between 102A and 102C), 120B (between 102Band 102C), and 120C (between 102C and 102D). These data connections areshown in bold solid lines to indicate such data connections acting astemporary data tunnels. Points 3, 4, 5, and 6 are the same as describedwith reference to FIG. 3 except that during this time data arriving fromAPN 101 that is destined for PDN-GW 102C is then forwarded to the PDN-GWthat is taking over active service for the NRI from which the data isreceived. In this way, data coming from the NRIs will arrive at theproper PDN-GW before the RIP is updated at point 6. Information comingfrom the SGW pool 103 may either be sent on to the corresponding NRIwithout forwarding to the newly active PDN-GW for that NRI or it may beforwarded to the newly active PDN-GW for that NRI until the NRI maps areupdated at point 5. In this way, the bringing down of PDN-GW 102C occurstransparently to the UE devices 106 and without incurring serviceinterruption. Point 7 indicates that the temporary data tunnels areremoved and the PDN-GW 102C is brought down after all corresponding UEsessions have been activated, new standby UE sessions have been created,and the RIP information has been exported to the APN.

FIG. 5 is a block diagram illustrating the resulting PDN-GW pool 102after the operations shown in FIGS. 3 and 4 have been performedaccording to embodiments of the invention. FIG. 5 is identical to FIG.1A except that PDN-GW 102C is inactive (in a non-operational state). InFIG. 5, each of the operational PDN-GWs 102A, 102B, and 102D hasadditional active and standby UE sessions (as described in FIGS. 3 and4) corresponding to activated UE sessions and newly created standby UEsessions.

FIG. 6 is a block diagram illustrating PDN-GW pool 102 responsivebringing up an inactive PDN-GW (e.g., adding a new PDN-GW, replacing aPDN-GW that entered a non-operational state, or restoring a PDN-GW thatentered a non-operational state) according to embodiments of theinvention. FIG. 6 is identical to FIG. 5 except that PDN-GW 102C hasgone from a non-operational state to an operational state and includes aplurality of points/operations and change indications that occur inresponse to the operational state of PDN-GW 102C. At point 1, PDN-GW102C becomes operational and available for participation in the PDN-GWpool 102. Responsively, it is determined which of the NRIs PDN-GW 102Cwill take responsibility for as the active PDN-GW (and thus, the UEsessions associated with those NRIs); as well as, in embodiments thatsupport standby UE sessions, which of the NRIs PDN-GW 102C will takeresponsibility for as the standby PDN-GW (and thus, the UE sessionsassociated with those NRIs). The entity making these determinations maybe different in different embodiments (e.g., it may be PDN-GW pool 102or it may be MME's 115 session resilience module 116). In FIG. 6, it isdetermined that PDN-GW 102C will become the active PDN-GW for NRIs 1, 3,and 9 and will become the standby PDN-GW for NRIs 4, 6, and 10. At point2, temporary data tunnels are established between each PDN-GW 102A,102B, and 102D that is an active and/or standby PDN-GW for NRIs whichPDN-GW 102C is assuming some responsibility as either active or standbyPDN-GW. These temporary data tunnels are established as previouslydescribed in FIG. 4. At point 3, the determined active and standbysessions are moved from PDN-GWs 102A, 102B, and 102D to PDN-GW 102C. Atpoint 4, the NRI map entries are updated as described with reference toFIG. 3 to indicate that PDN-GW 102C has assumed active or standbyresponsibility for the corresponding NRIs. At point 5, the APN sliceroutes are updated as described with reference to point 6 in FIG. 3. Atpoint 6, the temporary data tunnels are removed and the PDN-GW pool 102is finished bringing up PDN-GW 102C as an operational participant in thePDN-GW pool 102. While the PDN-GW 102C is being brought up, datacorresponding with UE sessions that are moving from a first activePDN-GW to PDN-GW 102C is forwarded to PDN-GE 102C across the temporarydata tunnels in the same way as described with reference to FIG. 4.

FIG. 7 is a block diagram illustrating a system including a PDN, a SGWpool, and a plurality of PDN-GWs (with one being shown in an explodedview) for providing N+M pooled session resilience according toembodiments of the invention. The first PDN-GW, such as PDN-GW 102A fromFIG. 1A, is coupled to one or more PDNs 190, each PDN assigned an APNand a plurality of IP addresses. Each APN sliced into a plurality of APNslices, such as APN slices 101A-101P, that are assigned a subset of theplurality of IP addresses for that PDN. The first PDN-GW 102A is furthercoupled to one or more other PDN-GWs, such as PDN-GWs 102B-102D, and iscoupled to a SGW pool 103. The first PDN-GW 102A comprises a pluralityof ports 715A-715Z, a session resilience module 716 that is coupled tothe plurality of ports 715A-715Z, a processor 720, and a memory 730. Theprocessor 720 (single or multi core; and if multi core, symmetrical orasymmetrical cores) may be of any type of architecture, such as CISC,RISC, VLIW, or hybrid architecture. The processor 720 may also include avariety of other components, such as a memory management unit and mainmemory bus interface(s). Furthermore, the processor 720 may beimplemented on one or more die within the same chip. While thisembodiment is described in relation to a single processor PDN-GW, otherembodiments are multi-processor PDN-GWs. The memory 730 and data trafficrepresents one or more machine-readable media. Thus, machine-readablemedia include any mechanism that provides (i.e., stores and/ortransmits) information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium may bemachine-readable storage media (e.g., magnetic disks; optical disks;random access memory; read only memory; flash memory devices),machine-readable communication media (e.g., electrical, optical,acoustical or other form of propagated signals—such as carrier waves,infrared signals, digital signals, etc.); etc.

In one embodiment, the session resilience module 716 is a sub-modulewithin a processor 720 while in other embodiments the session resiliencemodule 716 is a separate module that is coupled to the processor 720.The session resilience module 716 is configured to receive informationcorresponding to UE sessions which the first PDN-GW 102A is servicing asthe active PDN-GW upon the initiation of PDN connections. The sessionresilience module 716 is configured to store the active UE sessioninformation and periodically transmit the active UE session informationto one of the one more other PDN-GWs 102B-102D that are acting asstandby PDN-GWs for the UE sessions represented by the UE sessioninformation. In one embodiment, the session resilience module 716includes an active UE session module 716A that stores and maintains theactive UE sessions on the first PDN-GW 102A. In another embodiment, thesession resilience module 716 is coupled to the memory 730 and theactive UE session information is stored in memory 730.

The session resilience module 717 is further configured to receiveinformation corresponding to UE sessions which the first PDN-GW 102A isserving as the standby PDN-GW. The first PDN-GW 102A receives UE sessioninformation from one of the other PDN-GWs 102B-102D that is the activePDN-GW for that UE session. This information is kept in synchronizationon the first PDN-GW as a standby UE session so that the first PDN-GW102A can activate the standby UE session if and when the correspondingone of the other PDN-GWs enters a non-operational state. In oneembodiment, the session resilience module 716 includes a standby UEsession module 716B that stores and maintains the standby UE sessions onthe first PDN-GW 102A. In another embodiment, the session resiliencemodule 716 is coupled to the memory 730 and the standby UE sessioninformation is stored in memory 730.

The session resilience module 716 is further configured to recognizewhen a second PDN-GW enters a non-operational state and, in response, toactivate one or more of a plurality of standby UE sessions that are eachassociated with UE sessions on the second PDN-GW. Further, the sessionresilience module 716 is configured to notify the SGW pool 103 that thefirst PDN-GW 102A has activated the one or more of the plurality ofstandby UE sessions. The session resilience module 716 may beimplemented in hardware, software, or a combination of both.

In one embodiment, such as where the MME is not informing the PDN-GWsthat other PDN-GWs are entering the non-operational state, the firstPDN-GW 102A further comprises a heartbeat module 717 that is coupled tothe plurality of ports 715A-715Z. The heartbeat module 717 is configuredto transmit status inquiry messages to the one or more other PDN-GWs102B-102D and notify the session resilience module 716 when one of theone or more other PDN-GWs 102B-102D does not respond to the statusinquiry message. In response to the failure to respond, the sessionresilience module 716 can activate any standby UE sessions that areassociated with an active UE session on the failed PDN-GW. In anembodiment where the MME is informing the PDN-GWs that other PDN-GWs areentering the non-operational state, the MME would be performing theheartbeat functionality and the PDN-GWs would be coupled to the MMEthrough one of the plurality of ports 715A-715Z. Of course, the PDN-GW103A includes a variety of other components that are not shown in orderto avoid obscuring the invention.

FIG. 8 is a block diagram illustrating a system including a PDN-GW, a UEdevice, and a set of one or more SGWs (with one being shown in anexploded view) for providing N+W pooled session resilience according toembodiments of the invention. The first SGW, such as SGW 103A, iscoupled to one or more base stations 105 which further couple the firstSGW 103A with one or more UE devices 106. The first SGW is furthercoupled to a PDN-GW pool 102 and, optionally, to one or more other SGWs103B-103C. The first SGW 103A comprises a plurality of ports 815A-815Z,a session resilience module 818 that is coupled to the plurality ofports 815A-815Z, a processor 820, and a memory 830. The processor 820(single or multi core; and if multi core, symmetrical or asymmetricalcores) is of any type of architecture, such as CISC, RISC, VLIW, orhybrid architecture. The processor 820 may also include a variety ofother components, such as a memory management unit and main memory businterface(s). Furthermore, the processor 820 may be implemented on oneor more die within the same chip. While this embodiment is described inrelation to a single processor SGW, other embodiments aremulti-processor SGWs. The memory 830 further represents amachine-readable storage media.

In one embodiment, the session resilience module 818 is a sub-modulewithin a processor 820 while in other embodiment the session resiliencemodule 818 is a separate module that is coupled to the processor 820.The session resilience module 818 is configured to maintain a pluralityof UE sessions and maintain a NRI map. The NRI map, as described withreference to FIGS. 1-6, contains a plurality of NRI map entries. EachNRI map entry pertains to one or more UE sessions serviced by the SGWand includes information designating an active PDN-GW in the PDN-GW pool103 for the NRI associated with the one or more UE sessions. In oneembodiment, the NRI map entries further include information associatinga standby PDN-GW in the PDN-GW pool 103 with the corresponding NRI.However, in embodiments in which each NRI is assigned an individual IPaddress, it is not necessary for the NRI map entries to contain standbyPDN-GW information because the same address will be used in the eventthat the standby PDN-GW becomes the active PDN-GW for an NRI. In oneembodiment, the session resilience module 818 stores the NRI map entriesin the memory 830 while other embodiments include memory within thesession resilience module in which the NRI map entries are stored. Thesession resilience module 818 is configured to route traffic for each UEsession to the active PDN-GW designated in the NRI map for that UEsession's corresponding NRI. The session resilience module is furtherconfigured to receive notification that one of a plurality of PDN-GWs inthe PDN-GW pool 103 entered a non-operational state, and, in response,begin routing traffic previously destined to the non-operation PDN-GW toother PDN-GWs in the PDN-GW pool 103. In embodiments in which the NRImap contains information designating a standby PDN-GW for each NRI, thesession resilience module updates the NRI map entry to designate thestandby PDN-GW as the active PDN-GW for NRI map entries previouslydesignating the non-operational PDN-GW as the active PDN-GW. In thisway, upon receiving notification of the non-operational PDN-GW, thesession resilience module can switch to the standby PDN-GW for UEsessions associated with the non-operational PDN-GW. Further, thesession resilience module is configured to receive NRI map updatemessages that indicate active and/or standby PDN-GWs for one or moreNRIs. In response to receiving the NRI map update message, the sessionresilience module 818 updates the corresponding NRI map entries. Thesession resilience module 818 may be implemented in hardware, software,or a combination of both.

In one embodiment, where each SGW in the SGW pool 103 services activeand standby UE sessions (such as shown in FIG. 1B), the first SGW 103Afurther comprises a heartbeat module 819 that is coupled to theplurality of ports 815A-815Z. The heartbeat module 817 is configured totransmit status inquiry messages to the one or more SGWs 103A-102C inthe SGW pool 103 and notify the session resilience module 818 when oneof the one or more SGWs 103A-103C does not respond to the status inquirymessage. In response to the failure to respond, the session resiliencemodule 818 can activate one or more standby UE sessions for NRIsassociated with the failed SGW. In an embodiment where the MME isinforming the SGWs that other SGWs are entering the non-operationalstate, the MME would perform the heartbeat functionality and the SGWswould be coupled to the MME through one of the plurality of ports815A-815Z. Of course, the SGW 103A includes a variety of othercomponents that are not shown in order to avoid obscuring the invention.

ALTERNATIVE EMBODIMENTS

While the flow diagrams in the figures show a particular order ofoperations performed by certain embodiments of the invention, it shouldbe understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.).

While the invention has been described in terms of several embodiments,those skilled in the art will recognize that the invention is notlimited to the embodiments described, can be practiced with modificationand alteration within the spirit and scope of the appended claims. Thedescription is thus to be regarded as illustrative instead of limiting.

What is claimed is:
 1. A method performed in a first packet data network gateway (PDN-GW) in a PDN-GW pool, the PDN-GW pool for providing data connectivity between user equipment (UE) devices and an external PDN through an access point name (APN), wherein the first PDN-GW is coupled to a second PDN-GW and the method is for providing UE session resilience by allowing the first PDN-GW to provide connectivity for a set of one or more UE sessions previously serviced by the second PDN-GW after the second PDN-GW becomes non-operational, the method comprising the steps of: recognizing that the second PDN-GW is entering a non-operational state; establishing a temporary data tunnel with the second PDN-GW to be used by the second PDN-GW to forward data traffic received for the set of UE sessions to the first PDN-GW to prevent service interruption to the set of UE sessions through a graceful switchover; receiving, over the temporary data tunnel from the second PDN-GW, the forwarded data traffic of the set of UE sessions; activating a set of one or more standby UE sessions, wherein the set of standby UE sessions are synchronized copies of the set of UE sessions for which the second PDN-GW was the active PDN-GW, each of the set of UE sessions being associated with a UE device and a network resource identifier (NRI) that identifies an APN slice which corresponds with a subset of internet protocol addresses in the external PDN; transmitting a message to a serving gateway (SGW), the SGW for providing data connectivity between one or more of the UE devices and the PDN-GW pool, wherein the message indicates that the first PDN-GW has activated the set of standby UE sessions associated with one or more UE devices serviced by the SGW to cause the SGW to direct traffic previously bound for the second PDN-GW to the first PDN-GW; and closing the temporary data tunnel after the SGW begins directing the traffic previously bound for the second PDN-GW to the first PDN-GW, whereby UE session resilience is achieved in a PDN-GW pool by allowing the first PDN-GW to activate the set of standby UE sessions without notifying each of the UE devices associated with the standby UE sessions on the first PDN-GW and without causing service interruption to the set of UE sessions.
 2. The method of claim 1, wherein the message transmitted to the SGW indicates a plurality of NRIs, each NRI associated with one or more of the set of standby UE sessions associated with a UE device serviced by the SGW.
 3. The method of claim 1, where the message transmitted to the SGW is a NRI map update message that indicates updates to a plurality of NRI map entries, each NRI map entry indicating an active PDN-GW and a standby PDN-GW for a particular NRI and the NRI map update message includes entries corresponding to NRIs associated with one or more of the set of standby UE sessions.
 4. The method of claim 1, further comprising updating the data route between the APN slices associated with the NRIs of the set of standby UE sessions.
 5. A method performed in a serving gateway (SGW), the SGW for providing data connectivity between user equipment (UE) devices and a packet data network gateway (PDN-GW) pool that provides data connectivity between an external PDN and the SGW, wherein the SGW is coupled to a first PDN-GW and a second PDN-GW in the PDN-GW pool and the method is for providing UE session resilience by allowing the SGW to reroute traffic between the PDN-GW pool and UE device from the first PDN-GW to the second PDN-GW, the method comprising the steps of: creating a network resource identifier (NRI) map by inserting a plurality of NRI map entries including a first NRI map entry, wherein the first NRI map entry associates a first NRI with the first PDN-GW as an active PDN-GW for the first NRI, wherein the first NRI is associated with a first slice of an access point name (APN) that corresponds with a subset of internet protocol addresses in the external PDN, wherein the UE device is in communication with the first slice of the APN, wherein the creating of the NRI map further comprises associating the first NRI with the second PDN-GW as a standby PDN-GW for the first NRI; routing data traffic for a UE session to the first PDN-GW, wherein the UE session is for traffic between the UE device and the first slice of the APN; responsive to receiving one or more messages indicating that the first PDN-GW entered a non-operational state and that the second PDN-GW has assumed responsibility as the active PDN-GW for the first NRI and that a third PDN-GW has assumed responsibility as a standby PDN-GW for the first NRI: updating the first NRI map entry to indicate an association between the first NRI and the second PDN-GW as the active PDN-GW for the first NRI, routing data traffic for the UE session to the second PDN-GW; whereby UE session resilience is achieved by allowing the SGW to reroute data traffic from the UE device to an active PDN-GW without notifying the UE device of a change from the first PDN-GW to the second PDN-GW as the active PDN-GW.
 6. The method of claim 5, wherein the received one or more messages further indicate that the second PDN-GW has assumed responsibility as the active PDN-GW for UE sessions that are between the first NRI and UE devices communicating with slices in the APN associated with the first NRI.
 7. The method of claim 5 further comprising the steps of: associating each NRI map entry with a standby PDN-GW, wherein the first NRI map entry is associated with the second PDN-GW as the standby PDN-GW for that NRI and wherein a second NRI map entry is associated with the first PDN-GW as the active PDN-GW for that NRI; in response to the receiving of the one or more messages: determining a standby PDN-GW from the NRI map entries for all NRI map entries indicating that first PDN-GW is the active PDN-GW for those NRIs, and updating all NRI map entries indicating that the first PDN-GW is the active PDN-GW to indicate that the standby PDN-GW of each entry is now the active PDN-GW for that entry.
 8. A first packet data network gateway (PDN-GW) to be coupled to a second PDN-GW in a PDN-GW pool, the PDN-GW pool to provide data connectivity between an external PDN and a user equipment (UE) device, the first PDN-GW to provide UE session resilience by providing data connectivity for UE sessions previously serviced by the second PDN-GW after the second PDN-GW becomes non-operational, the first PDN-GW comprising: a processor; a set of one or more ports coupled to the processor and to be coupled to a serving gateway (SGW) pool; a memory coupled to the processor to store information for a plurality of active UE sessions and a plurality of standby UE sessions, each active and standby UE session to be associated with a UE device and a network resource identifier of an access point name (APN) slice, wherein the APN slice corresponds to a subset of Internet protocol (IP) addresses in the external PDN; and a session resilience module coupled to the memory to maintain the information for the plurality of active and standby UE sessions, the session resilience module configured to: recognize when the second PDN-GW is to enter a non-operational state, establish a temporary data tunnel with the second PDN-GW to be used by the second PDN-GW to forward data traffic to the first PDN-GW that is received for a set of one or more UE sessions that the second PDN-GW was the active PDN-GW for and that the first PDN-GW was the standby PDN-GW for, receive, over the temporary data tunnel from the second PDN-GW, the forwarded data traffic of the set of UE sessions, activate one or more of the plurality of standby UE sessions, each activated standby UE session to be associated with the second PDN-GW, notify the SGW pool that the first PDN-GW has activated the one or more of the plurality of standby UE sessions, and close the temporary data tunnel after the SGW begins directing the traffic previously bound for the second PDN-GW to the first PDN-GW; whereby UE session resilience is achieved in a PDN-GW pool by allowing the first PDN-GW to activate a plurality of standby UE sessions without notifying each UE device associated with a standby UE session on the first PDN-GW and without causing service interruption to the set of UE sessions.
 9. The first PDN-GW of claim 8, further comprising: a heartbeat module coupled with the set of one or more ports and the session resilience module, the heartbeat module configured to transmit a status inquiry message to the second PDN-GW and notify the session resilience module when the second PDN-GW fails to respond.
 10. The first PDN-GW of claim 8, wherein the session resilience module is further configured to: receive UE session data from the second PDN-GW corresponding to one or more of the plurality of standby UE sessions; and update the one or more of the plurality of standby UE sessions according to the received UE session data.
 11. A serving gateway (SGW) to be coupled to a user equipment (UE) device and a packet data network gateway (PDN-GW) pool comprised of a first PDN-GW and a second PDN-GW, the SGW to provide data connectivity between the UE device and the PDN-GW pool and provide UE session resilience by allowing the SGW to reroute traffic between the PDN-GW pool and UE device from the first PDN-GW to the second PDN-GW, the SGW comprising: a processor; a set of one or more ports coupled to the processor and to be coupled to one or more access point name (APN) slices, each APN slice corresponding with a subset of internet protocol addresses in the external PDN; a memory coupled to the processor to store a network resource identifier (NRI) map configured to store NRI map entries that associate a NRI with an active PDN-GW and a standby PDN-GW, wherein each NRI identifies one or more APN slices; and a session resilience module coupled to the memory, the session resilience module to maintain a plurality of UE sessions, maintain the NRI map, and configured to: create a first NRI map entry to associate a first NRI with the first PDN-GW as the active PDN-GW for the first NRI, route data traffic associated with the first NRI to the first PDN-GW, receive notification that the first PDN-GW entered a non-operational state, receive one or more NRI map update messages that are to indicate an update to the first NRI map entry, update the first NRI map entry according to the one or more NRI map update messages to associate the first NRI with the second PDN-GW as the active PDN-GW for the first NRI and to associate the first NRI with a third PDN-GW as the standby PDN-GW for the first NRI, and route data traffic associated with the first NRI to the second PDN-GW; whereby UE session resilience is achieved by allowing the SGW to reroute data traffic from the UE device to an active PDN-GW without notifying the UE device of a change from the first PDN-GW to the second PDN-GW as the active PDN-GW. 